The invention relates to an adjusting method for a rotary tablet press with a angle pulse encoder for evaluating the pressing force course on the individual punches in at least one pressing station, according to the introductory part of claim 1.
From EP 0 431 269 it is known, with rotary tablet presses to measure the maxima of each individual pressing with respect to the punch number and to compute for example the mean or the relative standard deviation. From the measuring results individual sortings-out and pressing force controls may be carried out.
From the mentioned document it is known, below the gear for the drive of the die plates to flange on a pulse encoder (angle encoder) which for example produces 3600 individual pulses per revolution. Furthermore per rotor revolution a rotation pulse is produced. With this an individual pulse corresponds to 0.1xc2x0 rotational angle of the rotor. The pulse encoder signals are supplied to a machine computer. With the help of the inputted punch number of the rotor this computer computes the number of angle pulses for the punch separation. Furthermore for each punch it computes a punch pulse with which a pressing force evaluation is carried out. The horizontal position of each punch during the compression phase is as a result known. The same applies to the pre-pressing station, which as is known is arranged at a fixed angle (pulse distance) to a main pressing station. Furthermore it is known, with a rotating rotor during the compression phase within a measuring window or over the whole signal course in the cycle of the angle pulses, for the analog pressing force signal to be measured and subjected to a maximum determination. The width of the measuring window corresponds as a rule to half the number of the angle pulses of a punch separation. The digitalised maximum value of the pressing force course is allocated to the associated punch number or the corresponding pressing station.
The scanning of the pressing force analog signal within a measuring window has the advantage that there is available a time reserve for further computations between the individual punches and that phase shiftings of the analog pressing force signal, which for example occur by a change in the speed or the pressing force, do not lead to measuring errors with the evaluation of the maximum.
The described method requires the exact adjustment of the angle pulse encoder relative to the rotor. The accuracy should be at least 0.1xc2x0 and is dependent of the fine touch of the person doing the adjusting. The angle pulse encoder is normally difficultly accessible and additional auxiliary means are required for the manual adjusting method, such as measuring punch, oscilloscope or likewise. Such an adjustment must be carried out during the end assembly or also later with a change of the angle pulse encoder. Such an adjusting method proceeds as follows:
A measuring punch is installed in the punch station for example No. 1 and is rotated visually as exact as possible below the middle of the main pressing station. The measuring punch is centered under pressing force. By hand the angle pulse encoder is rotated such that with this rotor position the pulse per revolution appears. Subsequently the screws for fastening the angle pulse encoder are carefully tightened in order not to lose the adjustment. With a rotating rotor the punch pulse is controlled for centricity to the pressing force with an oscilloscope. Subsequently there is effected a possible readjustment.
It is the object of the invention to specify a method with which a pressing force evaluation may be effected without a manual adjustment of the angle pulse encoder.
Expensive manual adjustment work is to be done away with and also the application of auxiliary means. On the other hand a high precision is to be achieved.
This object is achieved by the features of patent claim 1.
With the method according to the invention the angle pulse encoder is rigidly mounted in any position relative to the rotor shaft. Subsequently with the rotor the punch no. 1 is moved under the middle of a main pressing roller (the main pressing station). The movement may be effected by hand or with a crawling operation by a motor drive. It is essential that the punch is located approximately centrally below the main pressing roller, wherein a deviation may be +/xe2x88x92a quarter of the punch separation. With this the assembly of the remaining punches is not yet necessary. Alternatively already all punches may be assembled.
Subsequently the rotor by way of a command input at the operating computer is set in rotation, for example in crawling operation, until the pulse per revolution is produced. The number of pulses which are produced by this rotation up to the pulse per revolution are counted, and their number is stored in a machine computer (pulse offset). The machine computer computes the coarse positions, expressed in angle pulses, of all punches in relation to the pulse per revolution and produces on rotation of the rotor one coarse position pulse per punch. In the computer to each coarse position there is allocated a measuring window which extends to both sides of the coarse position. The allocation of a measuring window is, as already explained above, known per se.
From now the tablet press is set into operation, i.e. the punches must be installed and the material is supplied. From now, as is also known per se, in the measuring window or over the whole signal coarse per punch the pressing force course is scanned. As a result an angle-pulse-dependent pressing force coarse is obtained. The pressing force course by nature has a maximum and two minima. The punches are then located exactly below the middle of the main pressing roller when the pressing force maximum is produced or the two pressing force minima lie synmmetrically, i.e. the same angle pulse number, to the pressing roller middle. For determining the symmetry also the measuring points of the pressing force signal which lie above the minima are also suitable as long as both courses of the flanks behave equally. From the course of the pressing force as a result the computer thus evaluates the real punch position. This position as a rule does not correspond to the coarse position, but deviates from this by a distance of one or more angle pulses. The computer determines the deviations from the real and coarse position and evaluates from the individual deviations, which may indeed be different for the individual punches, a correction factor for determining the fine position of the punch. In other words the position pulse for the individual punches which previously had been determined from the coarse position, is from now on corrected by the correction factor.
If previously one has always spoken of one punch, then it is to be understood that with a tablet press usually in each case there are provided punch pairs, which together are arranged above and below a die plate and cooperate with a die opening.
For finding out a unambiguous correction factor the pressing force courses of all present punches may be taken into account and their frequency underlying this. If with this an unambiguous value stands out then it is used for the fine adjustment.
With a change of the rotor with another punch number the adjustment of the angle pulse encoder is not necessary. The evaluated angle pulse number, i.e. the result from the pulse offset and correction factor, may be stored in a computer. An adjustment is therefore only necessary with new machines or with the exchange of the angle pulse encoder.